Image not updating plot during animation

Question

The Problem:

I'm trying to simulate a live video by cycling through a series of still images I have saved in a directory, but when I add the animation and update functions my plot is displayed empty.

Background on why I'm doing this:

I believe its important for me to do it this way rather than a complete change of approach, say turning the images into a video first then displaying that, because what I really want to test is the image analysis I will be adding and then overlaying on each frame. The final application will be receiving frames one by one from a camera and will need to do some processing, display the image + annotations + output the data as .csv etc... I'm simulating this for now because I do not have any of the hardware to generate the images and will not have it for several months during which time I need to get the image processing set up, but I do have access to some sets of stills that are approximately what will be produced. In case its relevant my simulation images are 1680x1220 and are 1.88 Mb TIFFs, though I could covert and compress them if needed, and in the final form the resolution will be a bit higher and probably the image format could be adjusted if needed.

What I have tried:

• I followed an example to list all files in a folder, and an example to update a plot. However, the plot displays blank when I run the code.
• I added a line to print the current file name, and I can see this cycling as expected.
• I also made sure the images will display in the plot if I just create a plot and add one image, and they do. But, when combined with the animation function the plot is blank and I'm not sure what I've done wrong/failed to include.
• I also tried adding a plt.pause() in the update, but again this didn't work.
• I increased the interval up to 2000 to give it more time, but that didn't work. I believe 2000 is extreme, I'm expecting it should work with more like 20-30fps. Going to 0.5fps tells me the code is wrong or incomplete, rather than it just being a question of needing time to read the image file.

I appreciate no one else has my images, but they are nothing special. I'm using 60 images but I guess it could be tested with any 2 random images and setting range(60) to range(2) instead?

The example I copied originally demonstrated the animation function by making a random array, and if I do that it will show a plot that updates with random squares as expected. Replacing:

A = np.random.randn(10,10)
im.set_array(A)

...with my image instead...

im = cv2.imread(files[i],0)

...and the plot remains empty/blank. I get a window shown called "Figure1" (like when using the random array), but unlike with the array there is nothing in this window.

Full code:

import matplotlib.pyplot as plt
from matplotlib.animation import FuncAnimation
import os
import cv2

def update(i):
    im = cv2.imread(files[i],0) 
    print(files[i])
    #plt.pause(0.1)
    return im

path = 'C:\\Test Images\\'

files = []
# r=root, d=directories, f = files
for r, d, f in os.walk(path):
    for file in f:
        if '.TIFF' in file:
            files.append(os.path.join(r, file))

ani = FuncAnimation(plt.gcf(), update, frames=range(60), interval=50, blit=False)
plt.show()

I'm a python and a programming novice so have relied on adjusting examples others have given online but I have only a simplistic understanding of how they are working and end up with a lot of trial and error on the syntax. I just can't figure out anything to make this one work though.

Cheers for any help!

Answer 1

The main reason nothing is showing up is because you never add the images to the plot. I've provided some code below to do what you want, be sure to look up anything you are curious about or don't understand!

import glob
import os
from matplotlib import animation
import matplotlib.image as mpimg
import matplotlib.pyplot as plt

IMG_DIRPATH = 'C:\\Test Images\\'  # the folder with your images (be careful about
                                   # putting spaces in directory names!)
IMG_EXT = '.TIFF' # the file extension of your images

# Create a figure, and set to the desired size.
fig = plt.figure(figsize=[5, 5])

# Create axes for the current figure so that images can be sized appropriately.
# Passing in [0, 0, 1, 1] makes the axes fill the whole figure.
# frame_on=False means we won't have a bounding box, and setting xticks=[] and
# yticks=[] means that we won't have pesky tick marks along our image.
ax_props = {'frame_on': False, 'xticks': [], 'yticks': []}
ax = plt.axes([0, 0, 1, 1], **ax_props)

# Get all image filenames.
img_filepaths = glob.glob(os.path.join(IMG_DIRPATH, '*' + IMG_EXT))

def update_image(img_filepath):
    # Remove all existing images on the axes, and restore our settings.
    ax.clear()
    ax.update(ax_props)

    # Read the current image.
    img = mpimg.imread(img_filepath)

    # Add the current image to the plot axes.
    ax.imshow(img)

anim = animation.FuncAnimation(fig, update_image, frames=img_filepaths, interval=250)
plt.show()